To polymerize olefins Ziegler-Natta catalysts are used. These catalysts contain a procatalyst made from an internal electron donor, a titanium source, a magnesium source and a halogenating agent (which may be combined with one of the other components). The use of Ziegler-Natta catalysts is known where this procatalyst is combined with a cocatalyst and commonly with an external electron donor, or more commonly called an external selectivity control agent ("SCA"). See, e.g., U.S. Pat. No. 5,093,415 to Brady et al.
One class of electron donors taught by the art is veratrole (1,2-dimethoxybenzene) and certain derivatives thereof which incorporate additional substituents on the benzene ring, U.S. Pat. No. 4,971,936 to Wilson et al. See also U.S. Pat. No. 4,107,413 to Giannini et al. However, these specific compounds have certain deficiencies in that catalysts made with them have low catalytic activity (&lt;20 kg polymer/g procatalyst per hour) and produce polymers of low crystallinity (e.g., isotactic polypropylene with a xylene soluble of greater than 30% wt and a L.sub.(iso) (.sup.13 C NMR) of less than 50 even with a SCA). The use of these electron donor compounds solely to produce polymers of low crystallinity is confirmed in Japanese patent application Nos. 2613169 and H1-307519. It is desirable to find electron donors which result in catalysts of improved activity and selectivity.